Quartz is swept generally to render it largely insensitive to radiation. Sweeping generally involves subjecting a quartz crystal in air to an electric field of at least 250V/cm at a temperature of at least 400.degree. C. for a period of at least 12 hours. Such air-swept quartz in resonators commonly yields frequency offsets of no greater than 0.1 ppm after a cumulative exposure of 10.sup.6 to 10.sup.7 rad.
Sweeping only occurs when there is good electrical contact between the quartz and a metallic electrode. Many methods have been tried to improve the contact. For example, one method has been to sputter or evaporate the metal onto the quartz surface. This improves the contact, but if the metal is too strongly adherent, then hydrogen species including H.sub.2, H.sup.+, and H.sub.2 O cannot diffuse interfacially fast enough to cover the entire surface between the quartz and the metallic electrode. On the other hand, if the metal is weakly adherent, then metal recession results in loss of electrode contact during the prolonged sweeping times at high temperatures.